GREEN BAY - Cornerback Sam Shields revealed Tuesday on Instagram that he will be out at least eight more weeks, and the Green Bay Packers later announced they had placed Shields on injured reserve.

“I'm making great progress and hope to come back in 8 weeks and play this season,” Shields wrote on social media. “I will make a full recovery within that time frame #gopackgo”

Shields, the team’s No. 1 cornerback, will have to miss a minimum of eight weeks but is eligible to play again under the “designated to return” option each NFL team has at its disposal. The rule allows a team to bring one player back from injured reserve during the season provided he has missed a minimum of eight weeks.

Prior to the 2016 season, teams had to announce the designation ahead of time, before the player was placed on IR. The NFL since has amended that rule. Teams now place all injured players on IR and can decide who will receive the designation at a later date.

Shields suffered a concussion in the season opener against Jacksonville and has not practiced or played since. His time on injured reserve is not retroactive, so the soonest Shields would be eligible to play would be Week 15.

“The plan for Sam is to get him healthy, No. 1,” coach Mike McCarthy said at his news conference Tuesday morning, prior to the injured reserve announcement. “It's going to be longer than we might have expected. Just going off the last conversation I've had with Sam, it's just important to go one day at a time and make sure we get him healthy.”

Given the length of time Shields already has missed — Thursday’s game against Chicago will be his fifth — it’s possible general manager Ted Thompson regrets not placing him on IR in the immediate aftermath of the diagnosis. Had Thompson done so, Shields would have been eligible to return as early as Week 9, assuming he cleared the concussion protocol.

It was the fifth documented concussion of Shields’ career and his second in the last two seasons. Dating to last year, when he suffered a concussion against Dallas in December, Shields has missed eight of the last 10 games for the Packers.

“I think any time you’re dealing with concussions like in his situation,” defensive back Micah Hyde said, “one concussion, two concussions, 10 concussions, the knowledge we know about concussions now, it’s a serious situation and as many as he’s had we have to pray for him and hope everything is good.

“Him being my locker mate, I talk to him every day. Just fun to be around, great person on and off the field. It’s unfortunate but I know Sam, he’ll fight back. He’s a competitor. I wish him the best. He comes in all the time and still talks with us. It was good to have him around.”

The Packers needed a roster spot after trading for running back Knile Davis, who took part in practice Tuesday after arriving in Green Bay around 10 a.m. They are also expected to make one more roster move and promote running back Don Jackson from the practice squad.

Without Shields, the Packers face a potentially bare cupboard at cornerback against the Bears. Neither Damarious Randall (groin) nor Quinten Rollins (groin) took part in practice Tuesday, and there’s a legitimate chance both players will be unable to take the field this week.

If Randall and Rollins are inactive, the Packers likely will turn to LaDarius Gunter and Demetri Goodson as their top two corners, the same duo that finished the game against Dallas over the weekend.

Hyde, rookie Josh Hawkins and safety Morgan Burnett would be available to outfit the nickel and dime.

“Well, we’re going to be a work in progress there,” defensive coordinator Dom Capers said. “We’re playing some young guys. Obviously it’s good to get Goodson back. He’s got a little experience there. … I’ve got confidence in our young guys. We just have to go out and perform better than we did Sunday.”